Process of manufacturing thin ball grid array substrates

ABSTRACT

A process of manufacturing thin ball array substrates includes the steps of: using a layer of polyimide film as a carrier, electroplating a thin copper layer on the polyimide film, electroplating a thick copper layer on the thin copper layer, applying photosensitive coating layers on both sides of the carrier, mounting two masks with optically transmissible circuit tracks on two sides of the carrier and then processing the carrier with exposure treatment, processing the carrier with development treatment so as to remove the photosensitive coating layers aligned with the circuit track thereby forming recessed circuit tracks on the photosensitive coating layers, electroplating a copper layer on a top of the carrier thereby forming an additional copper layer on the thick copper layer, etching a bottom of the carrier to remove the upper recessed circuit track thereon, coating the copper layer on the upper recessed circuit track with soldering metallic material so as to make a top of the soldering metallic material, washing away the photosensitive coating layers with chemical agent, and removing surplus copper layer to remain in circuit lines and the soldering metallic material, whereby a thin ball grid array substrate with thicker circuit lines without remaining electroplating lines can be obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is related to a process of manufacturing thin ball gridarray substrates and in particular to one which can provide a thin ballgrid array substrate with thicker circuit lines without electroplatingbus lines remaining.

2. Description of the Prior Art

Lightness, thinness and compactness are requisites for portableelectronic devices, and so thin ball grid array substrates are widelyused in these devices for achieving these purposes. The conventionalprocess of manufacturing thin ball grid array falls into two categories,i.e. electrolytic electroplating and chemical electroplating.

The electrolytic electroplating process includes the following steps:

a. utilizing apolyimide film as a carrier 11;

b. forming a thin copper layer 12 on the carrier 11 by sputtering;

c. forming a thick copper 13 (which is thicker that the thin copperlayer 12) on the thin copper layer 12 by flash plating;

d. coating the top and bottom surfaces of the carrier 11 with a layer ofphotosensitive material 14;

e. mounting a mask 15 with optically transmissible circuit track 151 oneach of the top and bottom sides of the carrier 11, and then processingthe carrier with exposure treatment;

f. processing the carrier 11 with development treatment to remove thephotosensitive material aligned to the circuit track 151 thereby forminga recessed electrical circuit track diagram;

g. forming a copper layer 16 on the top surface of the carrier 11 byelectroplating so that the copper layer 16 is coated on the copper layer13 forming the recessed electrical circuit track with a top surface evenwith the photosensitive material layer 14;

h. etching the bottom of the carrier 11 so as to remove the polyimidefilm aligned with the circuit track of the mask 15;

i. washing away photosensitive material with chemicals;

j. removing surplus copper layer 13 resulting in the circuit lines 19and the electroplating bus lines 17 remaining (see FIG. 1l); and

k. connecting electroplating bus lines 17 to positive and negativeelectrodes of an electroplating apparatus to coat a metal layer 18 ofnickel, gold, or the like on the circuit lines 19.

Although the electrolytic electroplating process can provide thickercircuits and enables a manufacturer to select one of a number of metalsto coat on the copper circuit, the electroplating bus lines 17 willremain, thereby often causing delay in high speed signal transmission,producing noise, and attenuating signal energy.

The chemical electroplating process can form an additional coating ofnickel, gold, tin, or the like to cover the electroplating lines on thecircuit, but the coating thickness is limited. Accordingly, there is noprocess which can provide a thick circuit without electroplating buslines.

Therefore, it is an object of the present invention to provide a processof manufacturing thin ball grid array substrates.

SUMMARY OF THE INVENTION

This invention is related to a process of manufacturing thinf ball gridarray substrates and in particular to one which can provide a thin ballgrid array substrate with thicker circuit lines without electroplatinglines remaining.

It is the primary object of the present invention to provide a processof manufacturing thin ball array substrates which includes the steps of:using a layer of polyimide film as a carrier, sputtering a thinnercopper layer on the polyimide film, flash plating a thicker copper layeron the thinner copper layer, applying photosensitive coating layers onboth sides of the carrier, mounting two masks with opticallytransmissible circuit tracks on two sides of the carrier and thenprocessing the carrier with exposure treatment, processing the carrierwith development treatment so as to remove the photosensitive coatinglayers aligned with the circuit track thereby forming recessed circuittracks on the photosensitive coating layers, electroplating a copperlayer on a top of the carrier thereby forming an additional copper layeron the thicker copper layer, etching the bottom of the carrier to removethe upper recessed circuit track thereon, coating the copper layer onthe upper recessed circuit track with soldering metallic material so asto make a top of the soldering metallic material, washing away thephotosensitive coating layers with a chemical agent, and removing thesurplus copper layer to remain in circuit lines and the solderingmetallic material.

The foregoing object and summary provide only a brief introduction tothe present invention. To fully appreciate these and other objects ofthe present invention as well as the invention itself, all of which willbecome apparent to those skilled in the art, the following detaileddescription of the invention and the claims should be read inconjunction with the accompanying drawings. Throughout the specificationand drawings identical reference numerals refer to identical or similarparts. Many other advantages and features of the present invention willbecome manifest to those versed in the art upon making reference to thedetailed description and the accompanying sheets of drawings in which apreferred structural embodiment incorporating the principles of thepresent invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a, 1 b, 1 c, 1 d, 1 e, 1 d, 1 f, 1 g, 1 h, 1 i, 1 j and 1 killustrate the conventional electrolytic electroplating process ofmanufacturing thin ball grid array substrates;

FIG. 1l is a perspective view of FIG. 1f;

FIGS. 2a, 2 b, 2 c, 2 d, 2 e, 2 f, 2 g, 2 h, 2 I, 2 j and 2 k illustratethe process of manufacturing thin ball grid array substrates; and

FIG. 2l is a perspective view of FIG. 2f.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purpose of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings. Specific language will be used to describe same. It will,nevertheless, be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated herein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

The process of manufacturing thin ball array substrates according to thepresent invention comprises the steps of (see FIGS. 1a-1 k):

a. using a layer of polyimide film 21 as a carrier 2;

b. sputtering a thinner copper layer 22 on the polyimide film 21;

c. flash plating a thicker copper layer 23 on the thinner copper layer22 for providing a medium for electroplating thereafter;

d. applying photosensitive coating layers 24 and 25 of appropriatethickness on the top and bottom of the carrier 2;

e. mounting a mask 26 with optically transmissible circuit tracks 261 oneach of the top and bottom of the carrier 2 and then processing thecarrier 2 with exposure treatment (the pattern design of the photomaskdoes not have any superfluous electroplating bus line);

f. processing the carrier 2 with development treatment so as to removethe photosensitive coating layers 24 and 25 aligned with the circuittrack 261 thereby forming recessed circuit tracks 241 and 251 on thephotosensitive coating layers 24 and 25;

g. electroplating a copper layer 27 on the top of the carrier 2 therebyforming an additional copper layer on the copper layer 23 with a topslightly lower than that of the photosensitive coating layer 24;

h. etching the bottom of the carrier 2 to remove the recesses circuittrack 251 on the bottom, i.e. removing the polyimide film 11 not coveredwith the photosensitive coating layer 25;

i. coating the copper layer 27 on the recessed circuit track 241 withsoldering metallic material 29 (such as an alloy of tin and lead,63Sn/37Pb) so as to make the top of the soldering metallic material 29even with the top of the photosensitive coating layer 24 (the solderingmaterial 29 is also used as a copper etching resisting element);

j. washing away the photosensitive coating layers 24 and 25 with achemical agent;

l. removing surplus copper layer 23 resulting in circuit lines 3 (seeFIG. 2K) and soldering metallic material 29 remaining.

Finally, tin balls are provided on the soldering metallic material 29 sothat it is unnecessary to keep electroplating lines for coating nickelor gold on the circuit lines. The electroplating lines for coating thecopper layer 27 on the copper layer 23 are removed together with thecopper layer 23 at the step k of the process. Consequently, the presentinvention can provide a thin ball grid array substrate with thickercircuit lines without remaining electroplating lines.

It will be understood that each of the elements described above, or twoor more together may also find a useful application in other types ofmethods differing from the type described above.

While certain novel features of this invention have been shown anddescribed and are pointed out in the annexed claim, it is not intendedto be limited to the details above, since it will be understood thatvarious omissions, modifications, substitutions and changes in the formsand details of the device illustrated and in its operation can be madeby those skilled in the art without departing in any way from the spiritof the present invention.

What is claimed:
 1. A process of manufacturing thin ball arraysubstrates comprising steps of: a. using a layer of polyimide film as acarrier; b. electroplating a thin copper layer on said polyimide film;c. electroplating a thick copper layer on said thin copper layer forproviding a medium for electroplating thereafter, d. applying a firstphotosensitive coating layer on a top of said carrier and a secondphotosensitve coating layer on a bottom of said carrier; e. mounting twomasks with optically transmissible circuit tracks on two sides of saidcarrier and then processing said carrier with exposure treatment; f.processing said carrier with development treatment so as to remove saidphotosensitive coating layers aligned with said circuit track therebyforming a first recessed circuit track on said first photosensitivecoating layer and a second recessed circuit track on said secondphotosensitive coating layer; g. electroplating a copper layer on a topof said carrier thereby forming an additional copper layer on said thickcopper layer with a top slightly lower than that of said firstphotosensitive coating layer; h. etching a bottom of said carrier toremove said second recessed circuit track thereon, i.e. removing saidpolyimide film not covered with said second photosensitive coatinglayer; i. coating said copper layer on said first recessed circuit trackwith soldering metallic material so as to make a top of said solderingmetallic material even with a top of said photosensitive coating layer;j. washing away said photosensitive coating layers with a chemicalagent; k. removing the surplus copper layer resulting in the circuitlines and said soldering metallic material remaining.